The aim of this proposed research is to further investigate sphingomyelinase activity in human liver, spleen, brain and cultured skin fibroblasts. A deficiency in total sphingomyelinase activity has been implicated as the primary enzymatic defect in Types A and B Niemann-Pick disease (NPD). There are other types of sphingomyelin lipidosis that may or may not be classified as variants of NPD. The activity for sphingomyelinase will be measured with C14-labeled sphingomyelin which has been in use in this laboratory for over three years to diagnose NPD, to identify suspected carriers, to do prenatal diagnosis, and as a control enzyme in our studies on human beta-galactosidases, beta-glucosidases and other lysosomal enzymes. We will study the organ specificity and subcellular distribution of this activity using previously frozen tissues from both controls and patients who had NPD. Sphingomyelinase activity will be purified and, if possible, separated into isozymic forms using classical (gel chromatography, ion exchange chromatography, selective precipitation, etc.) and newer (affinity chromatography, isoelectric focusing) methods of procedure. An especially interesting and serious problem is finding the reason for storage of sphingomyelin in those cases having normal total sphingomyelinase activity. The reasons that will be examined include presence of an inhibitor of this activity in the patients' tissues, possible failure to localize the activity within the lysosome over synthesis of sphingomyelin or the possibility that this sphingomyelin storage is secondary to another metabolic lesion unrelated to sphingomyelinase. The properties of the residual activity remaining in some patients with NPD will be studied and compared to controls and other patients. Antibodies will be prepared to the sphingomyelinase activities and the relationship to the various other forms and between patients will be examined by immunochemical techniques. Patients with all types of NPD and some carriers (over 40 in all) are already available in our tissue culture bank and they await further detailed study. This study will tell us more about the role of sphingomyelinases in maintaining a normal balance of sphingomyelin and other membrane components.